This invention relates generally to a preform for forming a blow molded plastic bottle having an integral champagne base including a continuous standing ring circumscribing a central push-up region. More particularly, this invention focuses on diminishing the total mass of plastic necessary to form such a bottle while retaining the strength necessary in the bottom to prevent eversion of the base due to internal pressure within the bottle.
Blow molded plastic bottles having champagne-style bases for containing carbonated beverages and the like are well-known. Various features have been adopted in the past in order to enhance the strength of the base so as to resist the internal pressure caused by the carbonated beverage against the bottom tending to invert the central push-up region of the champagne base. One solution to resisting the inverting pressure has been the use of a large amount of resin in the base thereby making the base inflexible even under high internal pressure. This solution is cost-prohibitive for a non-return beverage bottle.
Another solution has been the use of radial ribs positioned on the inside of the push-up portion of the base and extending radially outward through the standing ring portion to merge with the outer sidewall of the bottle. An example of such a structure is shown in Krishnakumar, et al., U.S. Pat. Nos. 4,261,948 and 4,334,627. The formation of the interior ribs was achieved by forming axially elongated ribs on the interior of the preform which ribs were displaced from the preform molded position radially outward to the final position radially crossing the standing ring portion of the bottle.
Mahajan, U.S. Pat. No. 4,403,706 disclosed a further improvement in preform design which provided for hollow ribs to be formed which were restricted to the standing ring portion of the container so as to add stiffness to the standing ring potion. The hollow ribs of Mahajan were said to be as strong as the solid ribs of Krishnakumar yet use a reduced amount of resin.
Beck, U.S. Pat. Nos. 4,780,257; 4,889,752; and 4,927,679 sought to enhance the strength of the standing ring portion of the bottle by producing an annular ring in the preform which was displaced outward and became resident in the standing ring portion, thereby enhancing the strength of that portion. Generally the amount of resin employed in the Beck design diminished gradually as one moved inward from the standing ring to a ring surrounding a small central region where the thickness again increased.
While each of the structures have provided for enhanced strength of the champagne base, the more recent trend toward thin-walling of containers so as to minimize the amount of resin employed to make a bottle has added emphasis to the fact that the portion of the container forming the push-up region is the most vulnerable to failure. Further, the failure mode is one of eversion of the material on the inside of the standing ring portion, particularly where that standing ring portion has been thickened in accordance with the general design of the Beck patents discussed previously.
Accordingly, it is an object of the present invention to provide for enhanced strength for the push-up region of the container by permitting overall light-weighting of the container.